This invention relates to ink ribbon cartridges for use with dot printers or the like, and more particularly, to an improvement in take-up and pinch rollers disposed in a cartridge housing receiving an endless length of ink ribbon therein for transporting the ribbon so as to expose a minor portion of the ribbon to the outside of the cartridge and for taking the ribbon from the outside to the interior of the housing to store the ribbon in a repetitively folded manner.
Ink ribbon cartridges for use with dot printers or the like generally accommodate an endless length of ink ribbon folded in a repetitive manner within a cartridge housing. A pair of take-up and pinch rollers are disposed in the housing approximately at its take-up port. The take-up roller is driven to transport the ribbon in concert with the pinch roller. Specifically, the rollers cooperate to pull the ribbon from within the housing through its supply port, expose a minor portion of the ribbon to the outside of the housing, and return the ribbon again to the housing such that a major portion of the ribbon is accommodated in the housing in a repetitively folded manner.
More specifically, an ink ribbon cartridge comprises a cartridge housing defining a chamber therein and having supply and take-up ports at opposite ends of the chamber and an opening remote from the chamber; an endless length of ink ribbon having a major portion received in the chamber in a repetitively folded manner and a minor portion extending from the outermost fold to the innermost fold of the major folded portion and passing from the supply port to the take-up port across the opening; a take-up roller disposed at said take-up port; and a pinch roller in frictional contact with the take-up roller, the ribbon extending between the take-up and pinch rollers; whereby the take-up roller is driven to rotate in concert with the pinch roller to frictionally transport the ribbon therebetween, thereby taking the ribbon out of the chamber through the supply port and returning it into said chamber through the take-up port.
Conventional rollers are formed by injection molding solid plastic materials such as polyamide resins and optionally, indenting the circumferential surface. Some plastic rollers of this type are inexpensive, high in dimensional accuracy, and free of problems such as temperature-variable performance and shape, and deterioration by ink. However, in rollers of this type, the adherence of ink to the roller surface often causes slippage of the ribbon being frictionally driven, and in addition, only a reduced length of ribbon can be received in the housing because of the reduced length of each fold or turn of the major folded portion. Ribbon cartridges for use with dot printers are required to house a maximum length of ribbon in a given cartridge chamber volume by the repeated folding of the ribbon. The drawback of the plastic molded rollers that the reduced length of each fold of the major folded portion limits the overall length of ribbon received in the housing is unacceptable for such ribbon cartridges. At present, rollers of NBR (acrylonitrile-butadiene rubber) are used as a substitute for the plastic molded rollers.
The solid NBR rollers allow the length of each fold of a major folded portion of ribbon to be increased, increasing the overall length of ribbon received and extending the life of the cartridge. These rollers, however, have poor temperature properties, and particularly, the rubber elasticity is drastically diminished at low temperatures, causing uneven ribbon transport and slippage. They can therefore be used only in a limited temperature range. Furthermore, since NBR has poor oil resistance, the NBR rollers tend to swell up with ink and deformed at the ribbon contacting area. A further shortcoming is that NBR rollers are uneven in quality because of variations in hardness and working dimensions developing during manufacturing. Such unevenness is detrimental to the driving of the ribbon.
Other materials of which rollers may be made include sponge rubber materials of urethane rubber, NBR, and polyvinyl chloride. Rollers of spongy NBR have drawbacks similar to those of the above-mentioned solid NBR rollers. Unevenness in quality is further magnified by the expansion of NBR into sponge. Rollers of spongy polyvinyl chloride have poor temperature properties, and are liable to deterioration on account of migration of a plasticizer from the polyvinyl chloride to ink or migration of ink to the polyvinyl chloride. They are also uneven in quality. Rollers of spongy polyurethane rubber are subject to distortion or strain under applied loads, causing them to drive the ribbon in an unstable manner. Furthermore, rollers formed from closed-cell spongy urethane rubber by casting have reduced dimensional stability, and are substantially nonuniform in cell distribution, weight and hardness. The use of the cast urethane rubber rollers is still unsatisfactory in ribbon driving because the ribbon tends to shift towards one side or the other of the rollers as it is being driven. On the other hand, sintered spongy urethane rubber having interconnecting cells is also nonuniform in weight and hardness because of the varying amount of particulate material or powder charged for a batch. Like the cast urethane rubber rollers, rollers of the sintered urethane rubber also perform unsatisfactorily in ribbon driving. In addition, the sintered spongy urethane rubber is readily damaged because of its reduced strength. Furthermore, these spongy urethane rubbers are generally thermoplastic and thus have undesirable temperature properties. They exhibit increased hardness at low temperatures. Thus, rollers made of this type of spongy urethane rubber become unstable when driving the ribbon at low temperatures. The use of thermosetting spongy urethane rubbers cannot ensure stable ribbon driving because they are nonuniform in cell distribution. None of the spongy urethane rubbers are fully satisfactory with respect to ribbon driving, particularly stable ribbon driving.